The present invention relates to a cable fixing point for fixing at least one cable and to an elevator for transporting at least one load carrier by means of at least one cable, which is movable in its longitudinal direction, with a cable fixing point for a cable end of the respective cable.
Cables provided for supporting and transporting load carriers (for example a car or a counterweight) in an elevator are usually held at the cable ends at cable fixing points and between the cable fixing points are movable at least in segments in their longitudinal direction along tracks which are controlled by means of a suitable guide device for the cables. The respective cable fixing points can, for example, be arranged or fastened at the roof or base of an elevator shaft or at a load carrier of the elevator. The guide device usually comprises one or more rollers, around which the cables must run during movement in the longitudinal direction thereof, particularly a drive roller by which the traction forces can be transmitted to the cables, and optionally deflecting rollers.
When the cables are moved in their longitudinal direction during operation of the elevator they can in certain circumstances execute at the same time a rotational movement about their longitudinal direction at the guide device. Rotation of the cable about its longitudinal direction can, for example, be produced at the guide device if the cable is disposed at the guide device under a “diagonal” tension and is moved under boundary conditions which allow rotation of the cable about its longitudinal direction. That is the case when the cable is disposed under tension in its longitudinal direction and in that case is guided at a guide surface (for example at the surface of a roller) in a direction which is not parallel, but which lies at an inclination relative to the longitudinal direction of the cable. In the case of a cable which is disposed under a tension acting in its longitudinal direction and is guided in a groove at the surface of a roller the diagonal tension is realized if, for example, the groove is arranged within a plane standing perpendicularly to the axis of rotation of the roller and the cable is not guided parallel to this plane. In these circumstances the cable cannot be guided exclusively at the base of the groove if the roller rotates about its axis of rotation and the cable is then moved in its longitudinal direction. Rather, the cable runs partly over the flanks of the groove and thus transversely to the groove and can in that case execute a rolling motion at the surface of the roller in the direction of the axis of rotation of the roller. The rolling motion of the cable is in that case accompanied in each instance by a rotation of the cable about its longitudinal direction.
Diagonal tension unintentionally occurs in elevators in certain circumstances, for example when the guide device for the cables and the cable fixing points in the case of mounting are not precisely aligned in such a manner that every cable is guided at the guide device in each instance parallel to the direction of tension. In other cases diagonal tension is unavoidable—and accordingly intended—due to the construction of the cable guide. The latter is the case, for example, when several cables are guided respectively adjacent to one another over a first roller and subsequently over a second roller, but the axes of rotation of the rollers are not arranged exactly parallel to one another. In this case in a given instance one of the cables can be so guided that it is not disposed under diagonal tension. However, the remaining cables necessarily stand under a diagonal tension at least one of the rollers.
Rotational movements introduced into a cable can in turn lead to twistings (torsions) of the respective cable or individual length segments of the respective cable about the respective longitudinal direction. This is the case when the cable in the event of rotational movement about its longitudinal direction is not uniformly rotated about the same angle over its entire length. As a rule, twistings of the cables are connected with torsional moments which the respective cable exerts on the guide device or the cable fixing points.
A length segment of the cable shall be termed a “cable segment” in the following.
If a cable twists, the structure of the cable can be changed, in some circumstances irreversibly. A cable usually consists of several tensile carriers which are “stranded” together. Usually several tensile carriers—for example strands which are made of metallic wires and/or synthetic fibers and/or natural fibers—are each laid helically in a (tensile carrier) layer or several (tensile carrier) layers about a centrally arranged tensile carrier. In this manner the tensile carriers of a tensile carrier layer form a periodic arrangement which repeats each time in the same manner in the longitudinal direction of the cable respectively after a characteristic distance (the “lay length”). In the case of twisting of the cable about its longitudinal direction the relative arrangement of the tensile carriers can in certain circumstances be irreversibly changed and the cable damaged in that case. In the case of twisting of a cable, in particular, the lay length of the tensile carriers within a tensile carrier layer is shortened or extended.
The effect of twisting of a cable segment is, for the arrangement of the tensile carriers in the region of the cable segment, dependent on which rotational sense the ends of the cable segment are twisted relative to one another. Twisting of a cable segment shall here be regarded as “twisting-up” when the twisting is connected with a shortening of the lay length of a tensile carrier layer in this cable segment. Correspondingly, a torsional moment which, introduced into the cable or a segment of the cable, causes shortening of the cable length shall be termed “twisting-up” torsional moment. Analogously, twisting of a cable segment is here termed “untwisting” when the twisting is connected with extension of the lay length of a tensile carrier layer in this cable segment. Correspondingly, a torsional moment which, introduced into the cable or a segment of the cable, causes extension of the lay length shall be termed “untwisting” torsional moment.
Cables can be damaged not only by excessive twisting-up, but also by excessive untwisting of a tensile carrier layer. Many cable constructions are particularly sensitive to untwisting of a tensile carrier layer, particularly relative to untwisting of the outermost tensile carrier layer. If, for example, cables disposed under the action of a tensile load are untwisted then the individual tensile carriers are always unevenly loaded by the tensile load. The most strongly loaded tensile carriers can be degraded to increased extent and, in a given case, destroyed. This effect can substantially reduce the service life of a cable.
In an elevator, rotational movements of the cables should accordingly be so controlled that twistings or torsional moments, which in a given case are introduced into the cables, in each instance do not exceed a specific tolerable amount.
A cable fixing point for fastening at least one cable is shown in European patent document EP 1026115 A1, which comprises a respective cable end fastening for a cable end of the respective cable and a respective rotary mounting for the respective cable end fastening, wherein each rotary mounting comprises an axial bearing which enables rotation of the respective cable end fastening about a fixed, vertically arranged axis. Cable fixing points of that kind are used in an elevator in order to fix the ends of cables by which load carriers of the elevator are conveyed. The axial bearings ensure that the cables can freely rotate about their longitudinal direction at the cable fixing points. In this case the cables are in each instance so held at the cable fixing points that no torsional moment is introduced into the respective cable at the cable fixing points. The latter shall have the effect that rotations and/or twistings and/or torsional moments which in certain circumstances are introduced 110 into one of the cables between the respective cable fixing points, for example during running around a drive pulley or deflecting rollers, can be conducted away into the axial bearings of the cable fixing points. In this manner it shall, in particular, be achieved that the extent of such twistings, which in certain circumstances are introduced into a cable segment of a cable adjoining a cable fixing point, is rapidly reduced again as a consequence of appropriate rotation of the cable ends. In this manner, in particular, the cable segments adjoining the fixing points shall be preserved.
The elevator shown in EP 1026115 A1 has a number of disadvantages, when a cable, which is fastened to the cable fixing point, of the elevator is guided so that the cable segment adjoining the cable fixing point runs not exactly vertically, but at a specific angle of inclination relative to the vertical. In this case the tension force acting on the cable and thus directed parallel to the longitudinal direction of the cable is introduced into the cable fixing point at the cable end fastening of the cable in a direction which is inclined with respect to the vertical by the stated angle of inclination. The size of the angle of inclination under these preconditions usually depends on the instantaneous position of the respective load carrier of the elevator and is thus changed during transport of the load carriers. These effects lead to several technical problems. On the one hand, the axial bearing connected with the cable end fastening of the cable is loaded radially relative to the axis of rotation of the axial bearing. The axial bearing can rapidly wear under the effect of radial forces unless expensive countermeasures are taken. Moreover, the cable is bent to the side at the cable end fastening and in that case may be strongly curved or kinked. The tensile carriers of the cable and in a given case further components of the cable (for example, an outer cable casing or an intermediate layer arranged between two different tensile carrier layers) are accordingly non-uniformly loaded by the tension force. A part of the tensile carriers is consequently loaded more than average and can accordingly degrade more rapidly. Due to the fact that the cable during transporting movements of the load carriers is constantly rotated about its longitudinal direction and thus at the cable fixing point constantly about the vertical axis of rotation of the axial bearing, the cable at the cable end fastening is loaded in reverse bending on each reversal of the travel direction of the load carriers. These reverse bendings similarly promote degradation of the cable. For example, the arrangement of the tensile carriers in the region of the cable end fastening can be reversibly changed by reverse bending and the cable thus damaged. A further problem is to be observed if the cable is not constructed so that it is absolutely free of rotation. In this case a tensile carrier layer of the cable can be twisted under the action of the tension load, since the axial bearing enables free rotation of the cable at the cable fixing point and cannot apply a torsional moment which could counteract the untwisting of the tensile carrier layer. This effect can even arise when the load carriers of the elevator are not transported.